There are a number of industries which depend upon the storage of raw materials for transport and later discharge at processing centres, which materials are of a character that requires expensive and inefficient processes to remove the material from its container.
In the honey industry, producers ship their honey to a few centrally located process plants for packaging for retailing. Honey is a supersaturated solution in which the dextrose component will crystallise in the presence of impurities providing nuclei for crystal formation. The impure nature of the produce, and the vibration attendant to transport, usually results in the honey which is delivered to a processing plant being in a solidified state. If containers are to be reused so as to reduce costs, and if the honey is to be processed and bottled, it must be first liquified to remove it from its shipping containers. Liquidification usually takes place by storing the containers at an elevated temperature for times sufficient for the crystallised sugar to go back into solution. The energy comsumption required at this stage of processing is considerable. Present techniques are wasteful and a more efficient process is desirable.
Another material which is transported in quantity ,and which will solidify in the process, is tallow. To effect discharge, containers have been devised with heating coils to maintain the tallow in a liquid state but these are expensive.
Bitumen is a highly viscous material which may only be removed effectively from its containers by heating to temperatures in the vicinity of 200 C. Other viscous liquids which are commonly transported, and are heated to effectively remove them from their transport containers, are molasses, coconut oil, paints and resins.
The usual container employs a metal casing with a discharge outlet. If a viscous material in the simplest of containers, such as the common `44 gallon` drum, is to be heated, hot rooms, hot baths, thermal jackets, must be provided, with the capacity to receive one or more containers therein. Where heat is provided in this way, externally, the size of the container is limited by practical considerations associated with its movement. The container size might be readily increased with provision of internal heat exchange structures. The latter development raises the costs of the containers, and practice indicates that the lifetime of the container is reduced by association of the additional elements, and that there are more complex problems in the cleaning of the containers.